Concerning the Calculation of Inflow Performance of Wells Producing from Solution Gas Drive Reservoirs

Abstract

Estimating probable flow rates of wells producing from solution gas drive reservoirs is a problem frequently encountered by petroleum engineers. One approach to an answer involves the simultaneous solution of the well's inflow performance relationship (IPR) and the rate-dependent pressure losses in the well tubing, surface flow lines, and chokes. Nind covers very nicely several graphical methods of accomplishing the simultaneous solution. This note presents relationships that can be used to obtain IPR presents relationships that can be used to obtain IPR curves applicable to bounded solution gas drive reservoirs in which the average reservoir pressure is less than the reservoir fluid bubble-point pressure. Vogel's dimensionless IPR equation is the basis for the development. An example illustrates how future IPR curves can be developed from a current productivity index value. Vogel developed a general dimensionless relationship for wells producing under conditions outlined above and under pseudosteady-state conditions given by Eq. 1. (1) = 1 - 0 .2 - 0 .8 , where qo = stock-tank oil producing rate, B/D pwf = wellbore flowing pressure, psi pwf = wellbore flowing pressure, psip = average reservoir pressure, psi p = average reservoir pressure, psi qo max = maximum rate the well would producefor conditions of pwf = 0. Eq. 1 can be rearranged to = ...............(2) The productivity index of a well is defined by (3) J = Substitution of Eq. 3 into Eq. 2 yields (4) J = Physical conditions inherent in Eq. 4 are that reservoir Physical conditions inherent in Eq. 4 are that reservoir gas and oil saturations, as well as reservoir pressure, vary with distance away from the wellbore, and that the well's skin factor is zero. Let us now consider the situation in which fluid saturations are the same everywhere in the reservoir. This is analogous to a "zero drawdown" situation. Let J* be the well's productivity index under these conditions. Mathematically, (5) lim J J* = Applying the limit conditions to Eq. 4 yields (6) J* = P. 1141